USB RS232 Shenanigans (Updated 2025-05-28)

Fri, 18 Aug 2023 00:00:00 0000

I spent some time today testing out a couple of RS232 adapters with various bits of Psion software. I wanted to write a quick summary of what works and what doesn’t.

Software	CH340	PL2303TA	PL2303RA	FT232R
plptools (Linux)	Yes	Yes	Yes	Yes
PsiWin 2.3 on XP in VirtualBox (adopted USB)	Yes	Yes	No	Yes
PsiWin 2.3 on XP in VirtualBox (via virtual serial)	Not tested	Yes	No	Yes
PsiWin 1.1 on XP in VirtualBox (via virtual serial)	Not tested	Yes	Yes	?
MCLINK or SDBG in DOSBox Staging	Unreliable	Yes	Yes	No

Notes

CH340

Seems to work in most places, but DOSBox and DOSBox Staging are very unreliable with it. It’s very cheap and up until recently was what I recommended, but as I’ve tried to use SDBG for debugging on real hardware, I’ve needed something more reliable.

PL2303TA

Great all-rounder so far! I’ve been using an adapter by UGREEN with this chip in, and it’s been solid.

There’s just one problem. Prolific discontinued the chip in 2020. Getting drivers to work in newer versions of Windows is a pain. This won’t affect you if, like me, you’re not running anything newer than Windows 7. Modified versions of older drivers are out there to make the adapter work on Windows 11. Also, stocks will probably run out in the not-too-distant future. Linux, of course, works fine with it.

PL2303RA

I really wanted this to work with everything. You can get boards very cheaply from AliExpress, and my plan was to create two all-in-one Psion RS232 cables - one with a 9 pin mini-DIN for the older machines, one with a Honda connector for the newer ones. But PsiWin 2.3 won’t talk to it.

FT232R (Updated 2025-05-28)

Interesting one. This adapter works really well with PsiWin 2.3.3 and plptools, even at 115200. However, It’s unusable with DOSBox at any baud rate - it starts off being incredibly laggy and then gives up (see screenshot below). But even better than that, trying PsiWin 1.1 in an XP VM with the adapter completely locked up my laptop! I may investigate this further in the future.

Conclusion

I really want to be able to recommend a good all-rounder for Psion work, no matter what you want to do with the device. The PL2303TA might well be that, but its EOL status might put people off. The PL2303RA was so close to being perfect, but the pickiness of PsiWin 2.3 has scuppered my plans.

It’s safe to say that you can pick pretty much any of these adapters if you want to use plptools on *NIX. Reconnect, a macOS wrapper for plptools, will also be fine if you have the right macOS drivers (be careful with the PL2303 chips!).

I will update this as and when I test more chips. As of May 2025, the UGREEN PL2303TA is still my adapter of choice for all-round Psion goodness.

In fact, I like the UGREEN adapter so much, I’ve hacked one apart and plan to solder it to a Honda cable when I get the chance.